Anatomic Terminology: Planes of section
Anatomic imaging terminology and conventions.
Anatomic ‘geography' is similar to earth geography in that there is a commonly understood convention for talking about location and orientation of structures. This is especially important in radiology because any image can be displayed in several ways including right/left orientation. By convention we assume that humans are in the ‘anatomic position', which is standing or lying supine with palms up. We are ‘looking at' them from the front so that their LEFT is to our right. The conventional anatomic references to location/direction are as follows:
CEPHALAD: towards the top of the head
CAUDAD: towards the feet
VENTRAL: towards the front
DORSAL: towards the back
LEFT and RIGHT: as usually understood
Here are a couple of pictures that might help...This dude is in the 'anatomic' position
The planes of section define three ways to ‘slice' the body as follows:
Transverse (X-Y)
Transverse (or axial) sections form a series of circumferential slices - rather like slicing the body into a series of pancakes and stacking them atop one another. Transverse sections run top to bottom (superior to inferior). Your chin is inferior to your forehead but superior to your knees. The terms cranial (as in the cranium of your head) and caudal (latin for 'tail') may be used interchangeably with superior and inferior. In the transverse (or axial) plane, where right and left should go depends on if we are looking from the head down or the feet up. The convention is to say we are looking from the feet up. This means that the patient's LEFT is to your right >>> and vice versa. Here is a transverse (axial) CT slice through a patient's chest with the patient's right and left clearly marked.
Coronal (X-Z)
Coronal sections follow front to back, as though cutting through a corona, or halo, around the head. In medical terms anterior means front, and posterior means back. A similar group of terms includes ventral (front), and dorsal (back). The following animation runs anteriorly from the nose to the posterior of the head. Coronal images are always displayed with the patients LEFT to your right, just like the transverse plane.
Sagittal (Y-Z)
Sagittal sections follow from one side of the body to the other - left to right, or right to left. In medical terms lateral means 'outside', and medial 'inside' in the sense of lying in the middle. Your nose is medial (and inferior!) to your eyes, while your ears lie lateral to both your eyes and nose. The following animation traverses through the body from the right shoulder to the left, and back again. For the sagittal plane, there is not a strict 'rule' about how to orient the image, except that we put the TOP of the image up! The anterior (front) can go to the right or left. Here the front is to your right.
POSITIONING FOR XRAYS
Almost all XRays are performed in the FRONTAL plane and many are supplemented with OBLIQUE or LATERAL views. For the FRONTAL plane, we refer to the direction that the XRay beam goes through the patient. Thus a POSTERIOR-ANTERIOR (PA) chest is done with the XRays entering the patient's back (posterior) and passing through to the front (anterior) where they strike the detector (film or charged plate). Here is how this is done:
PA upright chest XRay positioning
Here is how the resulting XRay looks
PA upright chest XRay. Note that we dislpay with the patient's left to our right (as if we are looking at them in the anatomic position).
A lateral chest XRay gives an image equivilant to the sagittal plane. Here the XRays strike the patient's right side, pass through her, and strike the detector at her left. The 'skirt' she is wearing is made of lead to protect her ovaries from the radiation.
Positioning for upright lateral chest XRay
Here is what the image looks like
Upright lateral chest XRay. The lateral or sagittal plane does not have as strict a 'rule' for how to display the image as the transverse or frontal plane. Of course, for ALL three planes we like to put the head of the patient up! Here we orient the lateral chest XRay with anterior to the right but you will sometimes see it the other way and that is OK.
For the extremities, the terminology is the same but we can just have the patient put the affected part right on the detector. Here the patient is having an XRay of his right hand in the PA projection. The technologist (dark blue scrubs...by American Hospital Wear) is adjusting the XRay tube. The patient (light blue button down short sleeve shirt...by Van Heusen) has his right hand resting on the detector (film screen). Since the XRay passes from dorsum (posterior) to palm (anterior), we call this PA. If he were to supinate the hand (palm up), we would call this an AP film. We like the PA projection for hands because with palm up (AP), the fingers tend to curl (flex in doctor speak) and we want them to be flat (extended) for the XRay.
